Gastric glands are

gland A gland is a Cell (biology), cell or an Organ (biology), organ in an animal's body that produces and secretes different substances that the organism needs, either into the bloodstream or into a body cavity or outer surface. A gland may also funct ...

s in the lining of the

stomach The stomach is a muscular, hollow organ in the upper gastrointestinal tract of Human, humans and many other animals, including several invertebrates. The Ancient Greek name for the stomach is ''gaster'' which is used as ''gastric'' in medical t ...

that play an essential role in the process of digestion. Their secretions make up the digestive gastric juice. The gastric glands open into gastric pits in the

mucosa A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It ...

. The gastric mucosa is covered in surface mucous cells that produce the

mucus Mucus (, ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both Serous fluid, serous and muc ...

necessary to protect the stomach's epithelial lining from

gastric acid Gastric acid or stomach acid is the acidic component – hydrochloric acid – of gastric juice, produced by parietal cells in the gastric glands of the stomach lining. In humans, the pH is between one and three, much lower than most other a ...

secreted by

parietal cell Parietal cells (also known as oxyntic cells) are epithelial cells in the stomach that secrete hydrochloric acid (HCl) and intrinsic factor. These cells are located in the gastric glands found in the lining of the fundus and body regions o ...

s in the glands, and from

pepsin Pepsin is an endopeptidase that breaks down proteins into smaller peptides and amino acids. It is one of the main digestive enzymes in the digestive systems of humans and many other animals, where it helps digest the proteins in food. Pe ...

, a secreted

digestive enzyme Digestive enzymes take part in the chemical process of digestion, which follows the mechanical process of digestion. Food consists of macromolecules of proteins, carbohydrates, and fats that need to be broken down chemically by digestive enzymes ...

. Surface mucous cells follow the indentations and partly line the gastric pits. Other mucus secreting cells are found in the necks of the glands. These are mucous neck cells that produce a different kind of mucus. There are two types of gastric gland, the exocrine oxyntic gland, and the

endocrine The endocrine system is a messenger system in an organism comprising feedback loops of hormones that are released by internal glands directly into the circulatory system and that target and regulate distant organs. In vertebrates, the hypotha ...

pyloric gland. The major type of gastric gland is the oxyntic gland that is present in the fundus and the body of the stomach making up about 80 per cent of the stomach area. These glands are often referred to simply as the ''gastric glands''. The oxyntic gland contains the

s that produce

hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

and intrinsic factor, and chief cells that produce

pepsinogen Pepsin is an endopeptidase that breaks down proteins into smaller peptides and amino acids. It is one of the main digestive enzymes in the digestive systems of humans and many other animals, where it helps digest the proteins in food. Pe ...

and gastric lipase. The pyloric gland is found in the pyloric region, the remaining 20 per cent of the stomach. The pyloric glands are mainly in the

pyloric antrum The pylorus ( or ) connects the stomach to the duodenum. The pylorus is considered as having two parts, the ''pyloric antrum'' (opening to the body of the stomach) and the ''pyloric canal'' (opening to the duodenum). The ''pyloric canal'' ends a ...

. The pyloric gland secretes

gastrin Gastrin is a peptide hormone that stimulates secretion of gastric acid (HCl) by the parietal cells of the stomach and aids in gastric motility. It is released by G cells in the pyloric antrum of the stomach, duodenum, and the pancreas. ...

from its

G cell A G cell or gastrin cell is a type of cell in the stomach and duodenum that secretes gastrin. It works in conjunction with gastric chief cells and parietal cells. G cells are found deep within the pyloric glands of the stomach antrum, and occasi ...

s. Pyloric glands are similar in structure to the oxyntic glands but have hardly any parietal cells.

Types of gland

The gastric glands are glands in the lining of the stomach that play an essential role in the process of

digestion Digestion is the breakdown of large insoluble food compounds into small water-soluble components so that they can be absorbed into the blood plasma. In certain organisms, these smaller substances are absorbed through the small intestine into th ...

. All of the glands have mucus-secreting foveolar cells (also known as surface mucous cells) that line the stomach and partly line the gastric pits, and mucus-secreting mucous neck cells in the necks of the gastric glands.

Mucus Mucus (, ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both Serous fluid, serous and muc ...

lines the entire stomach as

gastric mucosa The gastric mucosa is the mucous membrane layer of the stomach, which contains the gastric pits, to which the gastric glands empty. In humans, it is about one mm thick, and its surface is smooth, soft, and velvety. It consists of simple secretor ...

protecting the stomach lining from the effects of

produced by the parietal cells and released from the oxyntic glands. Histology of normal antral mucosa

Gastric glands are mostly

exocrine gland Exocrine glands are glands that secrete substances onto an epithelial surface by way of a duct. Examples of exocrine glands include sweat, salivary, mammary, ceruminous, lacrimal, sebaceous, prostate and mucous. Exocrine glands are one of ...

s and are all located beneath the gastric pits within the gastric mucosa. The gastric mucosa is pitted with innumerable gastric pits which each house 3-5 gastric glands. The cells of the exocrine glands (oxyntic glands) are mucous neck cells, chief cells, and

s. Mucous neck cells produce mucus, parietal cells secrete

and intrinsic factor, chief cells secrete

and gastric lipase. The other type of gastric gland is the pyloric gland which is an

endocrine gland The endocrine system is a network of glands and organs located throughout the body. Along with the nervous system, it makes the neuroendocrine system, which controls and regulates many of the body's functions. Endocrine glands are ductless gland ...

that secretes the hormone

produced by its

Gastric juice

The secretions of the different exocrine gastric gland cells produce a watery, acidic fluid into the stomach lumen called gastric juice. Gastric juice contains water, hydrochloric acid, intrinsic factor, pepsinogen, and salts. Adults produce around two to three litres of gastric juice per day. The composition of the fluid varies according to the time of eating, and the rates of activity of the various cells. The cells are more active after eating. The composition of the gastric juice electrolytes is related to its rate of secretion: when secretion increases, the concentration of sodium decreases, and the concentration of hydrogen increases. There is always a higher level of potassium ions in the fluid than in the plasma.

Location

The glands are named for the region of the stomach that they occupy. The cardiac glands are found in the cardia of the stomach which is the part nearest to the heart, enclosing the opening where the esophagus joins to the stomach. Cardiac glands primarily secrete mucus. They are fewer in number than the other gastric glands and are more shallowly positioned in the mucosa. There are two kinds - either simple tubular with short ducts or compound racemose resembling the duodenal

Brunner's glands Brunner's glands (or duodenal glands) are compound tubuloalveolar submucosal glands found in that portion of the duodenum proximal to the hepatopancreatic sphincter (i.e sphincter of Oddi). For decades, it was believed that the main function of ...

. The fundic glands (or ''oxyntic glands''), are found in the fundus and body of the stomach. They are simple almost straight tubes, two or more of which open into a single duct. ''Oxyntic'' means acid-secreting and they secrete

(HCl) and intrinsic factor. The pyloric glands are located in the antrum of the

pylorus The pylorus ( or ) connects the stomach to the duodenum. The pylorus is considered as having two parts, the ''pyloric antrum'' (opening to the body of the stomach) and the ''pyloric canal'' (opening to the duodenum). The ''pyloric canal'' ends a ...

. They secrete

produced by their G cells.

Types of cell

There are millions of gastric pits (also known as ''foveolae'') in the gastric mucosa and their necessary narrowness determines the tubular form of the gastric gland. More than one tube allows for the accommodation of more than one cell type. The form of each gastric gland is similar; they are all described as having a neck region that is closest to the pit entrance, and basal regions on the lower parts of the tubes. The epithelium from the gastric mucosa travels into the pit and at the neck the epithelial cells change to short columnar granular cells. These cells almost fill the tube and the remaining lumen is continued as a very fine channel. Cells found in the gastric glands include mucous neck cells, chief cells,

s, G cells, and

enterochromaffin-like cell Enterochromaffin-like cells or ECL cells are a type of neuroendocrine cell found in the gastric glands of the gastric mucosa beneath the epithelium, in particular in the vicinity of parietal cells, that aid in the production of gastric acid via th ...

s (ECLs). The first cells of all of the glands are mucus-secreting foveolar cells that line the gastric pits. The mucus produced here is less acidic than that produced by the mucous neck cells. Fundic glands found in the fundus and also in the body have another two cell types–gastric chief cells and

s (oxyntic cells). * Foveolar cells (surface mucous cells) are mucus-producing cells which cover the inside of the stomach, protecting it from the corrosive nature of gastric acid. These cells line the gastric mucosa and follows into the gastric pits. * Mucous neck cells are located within gastric glands, interspersed between parietal cells. These are shorter than their surface counterpart and contain lesser quantities of mucin granules in their apical surface. Histology of gastric chief cell

* Chief cells (zymogen cells/peptic cells) – They are found in the basal regions of the gland and release proenzymes or zymogens –

(precursor to

), and prorennin (precursor to

rennin Chymosin or rennin is a protease found in rennet. It is an aspartic endopeptidase belonging to MEROPS A1 family. It is produced by newborn ruminant animals in the lining of the abomasum to curdle the milk they ingest, allowing a longer resid ...

or chymosin). Prorennin is secreted in young mammals (childhood stage). It is not secreted in adult mammals. Chief cells also produce small amounts of gastric lipase. Gastric lipase contributes little to digestion of fat. *

Parietal cell Parietal cells (also known as oxyntic cells) are epithelial cells in the stomach that secrete hydrochloric acid (HCl) and intrinsic factor. These cells are located in the gastric glands found in the lining of the fundus and body regions o ...

s ("parietal" means "relating to a wall"), also known as oxyntic cells are most numerous on the side walls of the gastric glands. The parietal cells secrete hydrochloric acid (

). This needs to be readily available for the stomach in a plentiful supply, and so from their positions in the walls, their secretory networks of fine channels called canaliculi can project and ingress into all the regions of the gastric-pit lumen. Another important secretion of the parietal cells is intrinsic factor. Intrinsic factor is a

glycoprotein Glycoproteins are proteins which contain oligosaccharide (sugar) chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known a ...

essential for the absorption of

vitamin B12 Vitamin B12, also known as cobalamin, is a water-soluble vitamin involved in metabolism. One of eight B vitamins, it serves as a vital cofactor (biochemistry), cofactor in DNA synthesis and both fatty acid metabolism, fatty acid and amino a ...

. The parietal cells also produce and release

bicarbonate In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula . Bicarbonate serves a crucial bioche ...

ions in response to

histamine Histamine is an organic nitrogenous compound involved in local immune responses communication, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Discovered in 19 ...

release from the nearby ECLs, and so serve a crucial role in the pH buffering system. * Enteroendocrine cells – They are usually present in the basal parts of the gastric glands, which is differentiated into three cell types – enterochromaffin like cells (ECL cells), G-cells, and D-cells. ** Enterochromaffin like cells (ECL cells) – They release serotonin and histamine. These cells store and release histamine when the pH of the stomach becomes too high. The release of histamine is stimulated by the secretion of

from the G cells. Histamine promotes the production and release of HCL from the parietal cells to the blood and protons to the stomach lumen. When the stomach pH decreases (becomes more acidic), the ECLs stop releasing histamine. ** G cells – They secrete

hormone. Gastrin stimulates the gastric glands to release gastric acid. These cells are mostly found in pyloric glands in the

; some are found in the duodenum and other tissues. The gastric pits of these glands are much deeper than the others and here the gastrin is secreted into the bloodstream not the lumen. ** D-cells – D-cells secrete

somatostatin Somatostatin, also known as growth hormone-inhibiting hormone (GHIH) or by #Nomenclature, several other names, is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G ...

. Somatostatin suppresses the release of hormones from the digestive tract.

Clinical significance

Fundic gland polyposis is a medical syndrome where the fundus and the body of the

develop many fundic gland polyps.

Pernicious anemia Pernicious anemia is a disease where not enough red blood cells are produced due to a deficiency of Vitamin B12, vitamin B12. Those affected often have a gradual onset. The most common initial symptoms are Fatigue, feeling tired and weak. Other ...

is caused when damaged parietal cells fail to produce the intrinsic factor necessary for the absorption of vitamin B12. This is the most common cause of

vitamin B12 deficiency Vitamin B12 deficiency, also known as cobalamin deficiency, is the medical condition in which the blood and tissue have a lower than normal level of Vitamin B12, vitamin B12. Symptoms can vary from none to severe. Mild deficiency may have fe ...

Additional images

File:Illu stomach layers.jpg, Layers of stomach wall File:Control-of-stomach-acid-sec.png, Gastric acid regulation Image:Gray1054.png, Human pyloric glands (at

)

References

External links

* - "Fundic stomach" * - "Mammal, ruminant stomach (LM, High)" * - "Digestive System: Alimentary Canal - fundic stomach"
Veterinary Histology at vt.edu
* - see slide #42 * - "Esophageal-stomach junction" * - "Digestive System: Alimentary Canal: esophageal/stomach junction" {{Authority control Digestive system Stomach